1. Field of the Invention
This invention relates to an oxygen concentration-detecting device for internal combustion engines, which detects the concentration of oxygen present in exhaust gases emitted from an internal combustion engine by using an oxygen concentration sensor arranged in the exhaust system of the engine.
2. Prior Art
Conventionally, a temperature control device for controlling the temperature of an oxygen concentration sensor arranged in the exhaust system of an internal combustion engine has been proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 60-235047, which accelerates heating of the oxygen sensor immediately after an ignition switch of the engine is turned on or a starter switch of the same is detected to be turned off, by maximizing electric power supplied to a heater of the oxygen sensor, thereby quickly activating the oxygen concentration sensor so as to start the air-fuel ratio feedback control at an early stage for improved exhaust emission characteristics of the engine.
The proposed temperature control device, however, suffers from the problem that when the heater is energized by supplying the maximum power thereto after the ignition switch is turned on, if the engine is not started with the ignition switch remaining on, the electric power stored in a battery of the engine continues to be consumed by the heater without generation of electric power by an alternator, resulting in a drop in the output voltage of the battery.
Further, when the engine is started under a low temperature condition, if the battery voltage is low, it can be difficult to start the engine by supplying the maximum electric power to the heater.